FIG. 1 illustrates a wind turbine 1. The wind turbine comprises a wind turbine tower 2 on which a wind turbine nacelle 3 is mounted. A wind turbine rotor 4 comprising at least one wind turbine blade 5 is mounted on a hub 6. The hub 6 is connected to nacelle 3 through a low speed shaft (not shown) extending from the nacelle front. The wind turbine illustrated in FIG. 1 may be a small model intended for domestic or light utility usage, or may be a large model, such as those that are used in large scale electricity generation or on a wind farm for example. In the latter case, the diameter of the rotor could be as large as 100 metres or more.
When building the structure of a wind turbine blade, where the structure mainly comprises fibre material and resin, in either a prepreg or infusion process, it is important to have a certain amount of fibres laying in a longitudinal direction of the blade to provide strength and stiffness in flapwise bending of the blade. Fibres are also needed in other directions to deal with twisting of the blade and general structural requirements.
Presently, e.g tri-axial fibre sheets are laid in the lengthwise direction on the blade, where at least one layer of fibres, normally the warp direction of a tri-axial fabric, is laid substantially parallel with the lengthwise direction of a blade or parallel to the leading edge or the trailing edge to actually provide the aforementioned strength and stiffness in flapwise bending.
However, due to the shape of the blade, which is very broad in the area around where maximum chord is located and very pointy at the tip of the blade, there is a massive amount of material waste when the sheets of uniform width are cut to conform to such a shape. This is because the sheets used are normally produced on a machine, which mass produces the sheet material, which after fabrication is rolled up to form large rolls of the sheet material. Often the precise cutting of the sheet material to be located in a certain position is done prior to the actual use of the sheet material, which increases lay-up speed, but at the same time increases material waste.
Retrieving the cut away material by splicing it to form a usable material has not been found feasible, as joints, like cut and overlay ends, have not shown proper strength performance. The typical joint shows only 50-60% strength of the original material strength.